This invention relates to liquid filtering apparatus, and particularly to filters of the so-called horizontal plate type.
Such filters, as described in U.S. Pat. No. 3,608,734 are commonly used for various industrial applications to cleanse large volumes of liquids such as coolants for metal rolling mills, metal can manufacturing lines and other metal working apparatus. Generally, they comprise a plurality of plate-like members which, when stacked together, form one or more filter chambers, each with an inlet for the liquid to be filtered. A layer of filter media is disposed between each adjacent pair of plates and space is provided under the media layer to trap the filtered liquid which then flows through outlet passages to a central storage container. The plate members are separable simultaneously to facilitate removal and replacement of the filter media after it has become clogged with deleterious filtered out material. Prior to separation of the plate members, the filter must be "blown-down". That is, all of the liquid within the filter chambers between the plate members must be removed so that no spillage occurs when the previously sealed plates are moved apart. In horizontal plate filters developed prior to the present invention, this "blow-down" procedure was relatively time consuming because such previous systems required essentially all of the liquid to be forced through the dirty filter media. This created serious problems, particularly where the filter apparatus comprised an essential link in an operating chain of equipment of a manufacturing facility such as a metal rolling mill. In such situations the time required to "blow-down" the filter and change its filter media was also costly "down" time for the manufacturing machinery itself. Additionally a rapid blowdown at elevated pressures will force dirt and tramp oil through the filer media into the clean coolant reservoir.